The present invention relates to an aerial vehicle controlled and propelled by oscillatory momentum generators and method of flying a vehicle and, more particularly, to the use of oscillatory momentum generators to sustain flight of a miniature or micro-miniature vehicle. The claimed invention is useful primarily in unmanned aerial vehicles (UAVs).
The aeronautical engineer has historically been faced with a tradeoff between physical storage space on an aircraft and the drag penalties associated with increasingly bluff bodies that inevitably accompany higher storage volumes. A classic example of this tradeoff is embodied by the C-130J that employs a ramp at the rear of a wide fuselage that introduces a moderate drag penalty.
In an attempt to resolve this disparity, Goldshmied (Goldschmied, F. R., xe2x80x9cFuselage Self-Propulsion by Static-Pressure Thrust: Wind Tunnel Verificationxe2x80x9d, AIAA Paper 87-2935, 1987.), studied the ideal shape of a thick body of revolution that employed suction as a means of Active Flow Control (AFC) that yielded low drag and high thrust efficiency and even demonstrated pressure thrust. Goldshmied further combined AFC with propulsion. Such a profile or body of revolution can serve the dual purpose of accommodating flow control actuators and utilizing them effectively for thrust, lift and moment control. Attitude Control can be gained and enhanced through distributed actuation or spatially differentiating the control authority to gain all three moments required for guidance.
Flying vehicles based upon the teachings of Goldshmied and Smith are known in the art. A further step in increasing the efficacy of flying vehicles could be achieved by combining the lifting, storing and controlling functions to a single structure, e.g. the flying wing.
For example, the propeller driven YB-35 flying-wing bomber conceptually designed by Sears (NORTHROPxe2x80x94an Aerodynamic History by F. Andersonxe2x80x94Northrop Press 1976) in the mid 1940""s had a range of 7500 miles and service ceiling of 40,000 ft. The Y-49 jet powered version was capable of cruising at 392 mph and reached 42,600 ft. Further examples include the B-2 flying wing bomber and so-called blended wing transport, (Liebeck, R. xe2x80x9cDesign of the blended-wing-body subsonic transport,xe2x80x9d AIAA Paper 2002-0002, 40th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nev., 2002). Thus the structural robustness, large inherent storage capability, low drag, potential for good aerodynamics with AFC offered by the Goldshmied profile incorporated into a flying-wing configuration have long been appreciated. Further, additional control authority obtained by relaxing the AFC on certain preselected areas of the configuration has the potential to allow the flow to separate from segments of the aft upper surface, allowing xe2x80x9cpush-pullxe2x80x9d control approaches. However, application of these principles to miniaturized aircraft has not previously been achieved because conventional flight cannot be achieved at these small scales and low velocities.
An unmanned aerial vehicle (UAV) is preferred over a conventional aircraft with a pilot whenever there is significant danger of loss of the aircraft (e.g. in warfare, extreme weather conditions, detection of hazardous materials or fire control operations). Typically, UAV""s have resembled small airplanes equipped with remote control or automated navigational systems. The navigational system may be, for example, via remote radio control or by a pre-programmed on-board computer and sensors suite. Such a UAV is costly, large and significantly looses efficiency when reduced in size, i.e. such that its wings operate at Reynolds numbers of 100,000 or smaller. Because the UAV does not need to carry a pilot, the payload is reduced and miniaturization becomes feasible. Recent advances in miniaturization of electronic, optic and sensing equipment serve to further reduce the required payload for a UAV. In theory, this should facilitate further miniaturization, and has indeed been attempted (e.g. McMichael, J M. and Francis, M. S. xe2x80x9cMicro Air Vehiclesxe2x80x94Toward a New Dimension in Flightxe2x80x9d, http://www.darpa.mil/tto/programs/mav.html).
However, this further miniaturization has not previously been successfully achieved because of the need to fly at large speeds to overcome the low efficiency imposed by the low Reynolds numbers. Additionally, these devices are extremely fragile due to their combined structural complexity and imposed weight limitations.
Typically, prior art UAV""s are propelled by rotors (e.g. U.S. Pat. Nos. 5,419,513; 5,277,380; and 5,575,438). This limits the degree of miniaturization, which can be implemented owing to torque forces about the axis of the rotor and it forces large empennage (which is even less efficient than the main wing due to the smaller size). In addition, the rotors themselves increase the fragility of the UAV, limiting the range of applications to which they are suited.
Thus, there is a great un-met need for an aerial vehicle controlled and propelled by oscillatory momentum generators and a method of flying a vehicle devoid of the above limitations.
According to one aspect of the present invention there is provided a vehicle capable of flight. The vehicle includes: (a) at least one wing; and (b) at least one oscillatory momentum generator mounted within the at least one wing. A thrust force from the oscillatory momentum generator directed outwards over the wing causes the wing to move so that a lift-generating air flow over a surface of the at least one wing is created.
According to another aspect of the present invention there is provided a method of flying a vehicle. The method includes: (a) providing on the vehicle at least one wing having at least one oscillatory momentum generator mounted therein; and (b) applying a thrust force from the at least one oscillatory momentum generator. The thrust force is directed outwards over the wing causing the wing to move so that a lift generating air flow over a surface of the at least one wing is created.
According to further features in preferred embodiments of the invention described below, the oscillatory momentum generator includes: (i) an internal cavity including an oscillatory jet ejection port, the jet ejection port being in communication with an environment exterior to the cavity; (ii) at least one oscillatable diaphragm designed and constructed to alternately decrease and increase a volume of the internal cavity; and (iii) an alternating electric current applicable to the at least one oscillatable diaphragm, the alternating electric current causing the diaphragm to oscillate, thereby expelling air through the jet emanation port and creating the thrust force.
According to still further features in the described preferred embodiments the oscillatory momentum generator further includes at least one electro-mechanical element designed and constructed to cause the diaphragm to vibrate at a frequency proportional to a frequency of the alternating electric current.
According to still further features in the described preferred embodiments the vehicle further includes an electric power source capable of supplying the alternating electric current.
According to still further features in the described preferred embodiments the thrust force is at least approximately 1 gram per watt of a power emanating from the power source.
According to still further features in the described preferred embodiments the oscillatory momentum generator operates at a resonance frequency thereof.
According to still further features in the described preferred embodiments the vehicle further includes an oscillation frequency sensor designed and constructed to sense oscillation of the diaphragm. Output from this sensor may be employed to cause the device to operate at its resonance frequency
According to still further features in the described preferred embodiments the vehicle further includes an attitude control system which operates by differentially regulating a thrust force applied by at least two of the at least one oscillatory momentum generators.
According to still further features in the described preferred embodiments the attitude control system regulates at least one parameter selected from the group consisting of roll, pitch and yaw.
According to still further features in the described preferred embodiments the vehicle further includes a launch assist device capable of imparting an initial velocity (vi) of approximately at least 10 m/s to the vehicle.
According to still further features in the described preferred embodiments the vehicle has a wingspan less than or equal to 45 cm.
According to still further features in the described preferred embodiments the at least one oscillatory momentum generator includes a plurality of oscillatory momentum generators arranged in at least one row along the at least one wing.
According to still further features in the described preferred embodiments the thrust force exits the oscillatory momentum generator at an angle of less than approximately 45 degrees with respect to the surface of the wing. Preferably, the thrust force is directed to a trailing edge of the wing.
According to still further features in the described preferred embodiments the applying the thrust force includes: (i) providing the oscillatory momentum generator, (ii) oscillating the at least one oscillatable diaphragm to alternately decrease and increase a volume of the internal cavity; and (iii) applying the alternating electric current to the at least one oscillatable diaphragm to cause the diaphragm to oscillate, thereby expelling an air stream through the jet emanation port and creating the thrust force. The generator includes an internal cavity, an oscillatory jet ejection port in fluid communication with an environment exterior to the cavity and with the cavity, at least one oscillatable diaphragm, and an alternating electric current;
According to still further features in the described preferred embodiments the applying the thrust force further includes: (iv) employing at least one electro-mechanical element designed and constructed to cause the diaphragm to vibrate at a frequency proportional to a frequency of the alternating electric current.
According to still further features in the described preferred embodiments the method includes providing an electric power source capable of supplying the alternating electric current.
According to still further features in the described preferred embodiments a thrust force of at least approximately 1 gram per watt of electric power emanating from the power source is achieved.
According to still further features in the described preferred embodiments the method further includes causing the oscillatory momentum generator to operate at a resonance frequency thereof.
According to still further features in the described preferred embodiments the method further includes employing an oscillation frequency sensor to sense oscillation of the diaphragm. An output of the oscillation frequency sensor is then employed to cause the oscillatory momentum generator to operate at a resonance frequency thereof.
According to still further features in the described preferred embodiments the method further includes controlling an attitude of the vehicle by differentially regulating a thrust force applied by at least two of a plurality of the at least one oscillatory momentum generators.
According to still further features in the described preferred embodiments the method further includes applying a launch force capable of imparting an initial velocity (vi) of approximately at least 10 m/s to the vehicle.
According to still further features in the described preferred embodiments the method further includes limiting a wingspan of the at least one wing to less than approximately exactly 45 cm.
According to still further features in the described preferred embodiments the method further includes deploying a plurality of the at least one oscillatory momentum generators in at least one row along the at least one wing.
According to still further features in the described preferred embodiments the method further includes directing the thrust force to exit the oscillatory momentum generator at an angle of less than approximately 45 degrees with respect to the surface of the wing.
The present invention successfully addresses the shortcomings of the presently known configurations by providing an aerial vehicle controlled and propelled by oscillatory momentum generators and method of flying same.
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.